扩展平均值以从数值泛型返回Double [英] Extension for average to return Double from Numeric generic

问题描述

假设我为同类数据列创建协议和结构:

Suppose I create a protocol and structure for a Column of homogeneously typed data:

protocol Columnizable {
    associatedtype Item

    var name: String { get }
    var values: [Item] { get }

}

struct Column<T>: Columnizable {

    var name: String
    var values = [T]()

}

我想创建一个协议扩展，允许Numeric具有 average 函数，该函数可以在类型符合 Numeric <的情况下计算 values 的平均值./code>协议-例如Double和Int

I would like to create a Protocol extension that allows Numeric to have an average function that could compute the average of values if the type conforms to Numeric protocol- for instance, namely Double and Int

extension Columnizable where Item: Numeric {

    func average() -> Double {
        return Double(sum()) / values.count
    }

    func sum() -> Item {
        return values.reduce(0, +)
    }

}

由于以下原因，我对 average 函数的尝试无法编译:

My attempt at the average function cannot be compiled because of:

无法为类型为'(Self.item)'的参数列表的类型为'Double'的初始化程序

尝试强制转换为Double无效.任何有关最佳做法的建议都将不胜感激.

Attempts to cast to Double do not work. Any advice for best practices here would be appreciated.

推荐答案

我需要使用 BinaryInteger 或 BinaryFloatingPoint 协议，因为它们可以轻松转换为双.正如@rob napier所说， Complex 类型将不是 Double 可转换的.

I needed to use the BinaryInteger or BinaryFloatingPoint protocols since they can easily be transformed to a Double. As @rob napier called out, that a Complex type would not be Double convertible.

extension Columnizable where Item: BinaryInteger {
    var average: Double {
        return Double(total) / Double(values.count)
    }
}

extension Columnizable where Item: BinaryFloatingPoint {
    var average: Item {
        return total / Item(values.count)
    }
}

stackoverflow.com/a/28288619/2019221

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